To determine which element will pair with a group 1 alkali metal like lithium (Li) in a 1:1 ratio based on trends in valence electrons, we need to consider how these elements bond chemically. Let's analyze each option:
1. Carbon (C)
- Carbon has 4 valence electrons. It usually forms covalent bonds and completes its octet by sharing four electrons. In compounds like methane (CH₄), carbon pairs with four hydrogen atoms. When pairing with alkali metals, it does not typically form a 1:1 ratio.
2. Barium (Ba)
- Barium is an alkaline earth metal with 2 valence electrons. It tends to lose two electrons to achieve a stable electron configuration, forming a Ba²⁺ ion. Barium would not readily form a 1:1 ratio with a group 1 metal because it requires pairing with two Li⁺ ions to balance its charge (forming something like Li₂Ba).
3. Nitrogen (N)
- Nitrogen has 5 valence electrons and typically forms N³⁻ ions by gaining 3 electrons to complete its octet. To balance with a group 1 alkali metal, such as lithium, you would need 3 Li⁺ ions to balance one N³⁻ ion, resulting in a formula like Li₃N. This is not a 1:1 ratio.
4. Chlorine (Cl)
- Chlorine has 7 valence electrons and typically gains 1 electron to form a Cl⁻ ion. This ion can easily pair with a single Li⁺ ion to form lithium chloride (LiCl), where the ratio of lithium to chlorine is 1:1.
Based on this analysis, the element that will pair with a group 1 alkali metal like lithium (Li) in a 1:1 ratio is chlorine (Cl). Therefore, the correct answer is:
4. Chlorine (Cl)
